The present invention relates generally to the internetworking of connectionless (e.g. Internet Protocol or xe2x80x9cIPxe2x80x9d) and connection oriented (e.g. ATM, MPLS, RSVP) networks, and, more particularly, to a technique that allows datagrams (messages) generated by source endpoints on a connectionless (CL) network to be redirected to destinations on a CL network via a communication path that includes a connection oriented (CO) network operated in a switched mode (as opposed to a provisioned mode) if there is an advantage from the user or service provider prospective.
Connectionless (CL) networks and connection-oriented (CO) networks have some fundamental distinguishing features. In CL networks, no explicit connection setup actions are executed prior to transmitting datagrams; instead, datagrams are routed through a series of interconnected nodes to their destinations based on information in their headers. CO networks operated in the switched mode (as opposed to the provisioned mode) are those in which connection setup for each call or session is performed prior to information transfer. (In a provisioned mode, the path through the network from a source to a destination is set up in advance, i.e., when the network is provisioned, and is not changed on a short term, i.e., call by call basis). In CO networks, connection setup actions consist of determining a route for the connection, allocating bandwidth (and possibly buffer) resources on the links and switches on the route, assigning and distributing xe2x80x9clabelsxe2x80x9d or xe2x80x9cpositionsxe2x80x9d (e.g., time slots or wavelengths) based on whether the CO network is packet or circuit switched, respectively, and programming connection information into switch fabrics and endpoints.
These two types of networks, CO and CL, enjoy advantages and disadvantages from both the user perspective and the service provider perspective. CL networks, for instance, do not suffer the delay and processing overhead associated with connection setup. In contrast, information about the connections in CO networks helps in providing service guarantees and, furthermore, makes it possible to most efficiently use network resources (e.g., bandwidth) by xe2x80x9cswitchingxe2x80x9d datagrams to appropriate connections as the connections are established.
The need to integrate and exploit the advantages of both CL and CO networks has long been recognized. Two examples are the use of SS7 (Signaling System No. 7) CL networks in conjunction with the CO telephony network, and the use of RSVP (Resource reSerVation Protocol) in IP networks. (See R. Braden, L. Zhang, S. Berson, S. Herzog, S. Jamin, xe2x80x9cResource ReSerVation Protocol (RSVP) Version 1 Functional Specification,xe2x80x9d IETF RFC 2205, September 1997) In both of these solutions, applications explicitly choose the networking mode appropriate to their needs.
Notwithstanding the need to integrate CL and CO networks, prior art approaches have heretofore not routed traffic from a source on a CL network onto a CO network operated in the switched mode (as opposed to a provisioned mode), because of the potential loss of datagrams during the time period when a path is being set up in the CO network. Specifically, if a transition between a CL network and a CO network occurs at a gateway, datagrams originating on the CL network and destined for a user continue to arrive at the gateway. These packets typically arrive every few microseconds, or less. During the time period when the path through the CO network toward the user is being set up, typically on the order of milliseconds, many datagrams will arrive at the gateway, and it is important that these datagrams not be lost. One possible solution, involving buffering of datagrams, has been suggested. However, this solution is generally impractical, since the size of the buffer would have to be very large.
In accordance with the present invention, nodes called CL-CO gateways, are arranged to have connectivity to both the CL network and the CO network. When CL traffic originating at a source reaches these gateway nodes, a decision is made whether to continue carrying the information in the CL mode, or to redirect the traffic to a CO network. In accordance with one embodiment of the present invention, each CL-CO gateway includes hardware and software modules that typically comprise (a) interfaces to the CO network, (b) interfaces to the CL network (c) a moderately sized packet buffer for temporarily storing packets waiting for CO network setup or turnaround; (d) a database for storing forwarding, flow control, header translation and other information, and (e) a processor containing logic for controlling the gateway packet handling operations. In accordance with another embodiment of the present invention, the gateway additionally includes a switch fabric for CO networking, a CL packet forwarding engine, and/or a protocol converter. Additionally, it is to be noted that the gateway of the present invention can be incorporated within a CL node, but not all nodes of the CL network need to have the ability to make redirect decisions.
In order to avoid the need for a large packet buffer and to also avoid the loss of datagrams, the gateway is arranged, in one embodiment of the present invention, to generate and transmit to the source of the datagrams, a signal requesting the source to slow down or stop transmission of datagrams during the time period when the gateway is establishing a path through the CO network. In another embodiment of the invention, datagrams received at the gateway are turned around and continue to be routed at least temporarily through the CL network during the period when the CO network path is being set up. As a further alternative, application or transport layer signals generated in the source are intercepted by the gateway and used to trigger connection setup in the CO network even before datagrams have been transmitted from the source, thereby assuring that when datagrams reach the gateway, there is no loss of information.
In the present invention, the CO network can be an MPLS (MultiProtocol Label Switching) or RSVP (Resource reSerVation Protocol) based IP network, a WDM (Wavelength Division Multiplexed) network, an ATM (Asynchronous Transfer Mode) network, or an STM (Synchronous Time Multiplexing) network, such as the telephony network or a SONET network. The CL network is typically, although not necessarily, an IP network. The present invention is useful, for example, in serving the needs of Internet users who want stricter quality-of-service guarantees for their file transfer application than is currently offered by the Internet.